Fe-doped NiO nanoparticles: Microscopic and Spectroscopic Characterizations

Ni1−xFexO single phase nanoparticles, synthesized by lyophilization and heat treatment, were characterized by microscopic and spectroscopic techniques searching for evidence of a core-shell structure. Transmission electron microscopy, X-ray photoelectron spectroscopy, and more extensively Mössbauer spectroscopy were applied in this study. Consistent with structural and magnetic analyses previously reported, these findings support the plausibility of a core-shell structure in Ni1−xFexO nanoparticles. The shell was found to be very thin and more iron-rich than the core. The core has a lower iron concentration than the nominal overall concentration. The nanoparticles were not completely magnetized at room temperature, but below 200 °C the iron moments froze almost completely.